1. Field of the Invention
The present invention generally relates to combustion systems, and, more particularly, to a method and apparatus for processing effluent vapors using catalytic oxidation.
2. Description of the Related Art
The regulation of hazardous air pollutants has become a prominent feature of governmental efforts designed to remedy the costly and adverse consequences arising from the industrial release of volatile organic compounds by an array of manufacturing activities and facilities such as wastewater treatment operations, storage vessels, process vents, and transfer operations. Industry has responded by developing a variety of combustion technologies aimed at the destruction of the hydrocarbon effluent at the service station vent. The combustion devices were proposed as an alternative to existing equipment that detected and isolated fugitive vapor emissions for storage but did not eliminate the hydrocarbon vapors. Current detection equipment includes sensor units, for example, that are employed to sense the presence of hydrocarbon vent emissions and facilitate their collection and subsequent disposal.
Thermal combustion is an example of one such combustion technology utilized by industry. However, this combustion process has several drawbacks. For example, thermal oxidation requires the combustion process to take place in a chamber at significantly elevated temperatures and for residence times that are sometimes difficult to sustain, particularly at high temperatures. Additionally, supplementary fuel is frequently required to initiate or sustain thermal combustion reactions that operate on hydrocarbon streams with low fuel content. This demand for supplementary fuel will only increase with the growing use of ORVR cars whose operation will result in progressively leaner hydrocarbon vent emissions.
What is therefore needed is a combustion technology that is amenable to destroying vapor effluents characterized by lean fuel concentrations. The system should also be capable of providing a measure of selectable control over the dilution level, and be compatible with industry-wide hazardous disposal guidelines.
The invention comprises, in one form thereof, a method and apparatus for oxidizing a mixture of air and fuel vapor. The amount of air provided for mixing with the fuel vapors is determined in accordance with the temperature of the oxidation reaction as measured by a temperature sensor. Controlling the dilution level in this manner provides an efficient vent processing design. The system is particularly used to process vapor emissions emanating from a vehicle fuel tank during refueling.
The invention comprises, in another form thereof, a combustion system for processing vapor effluents from a fuel receiving tank. A vapor collection means, which is disposed in vapor communicating relationship with respect to the storage tank, is provided in the combustion system for controllably collecting vapor effluents from the fuel receiving tank. The combustion system further provides an oxidation processing means for operatively oxidizing a vapor composition including hydrocarbon and oxygen; and sensor means for sensing a temperature associated with the oxidizing activity of the oxidation processing means. A vapor dilution means, which is responsive to the temperature sensed by the sensor means, is provided for controllably diluting the collected vapor effluents as a function of the sensed temperature to form a mixture including air and vapor effluents. A vapor transfer means is further provided for transferring the air-vapor mixture from the vapor dilution means to the oxidation processing means for oxidation therein.
The oxidation processing means further includes an oxidation catalyst. The sensor means further includes means for determining the temperature of the oxidation catalyst. The combustion system further includes, in another form thereof, a combustion chamber containing the oxidation catalyst, wherein the sensor means further includes means for determining the temperature within the combustion chamber.
The combustion system is operationally characterized, in another form thereof, wherein the level of vapor effluent dilution effectuated by the vapor dilution means is effective in controllably regulating the oxidation activity of the oxidation processing means such that the oxidation activity is controllably maintained within a selectable operating range.
The vapor dilution means comprises, in one form thereof, a dilution level determining means for determining an air concentration level for the vapor mixture as a function of the sensed temperature provided by the sensor means; and air supply means for supplying a controllable flow of air. A mixing means is provided for controllably combining, in accordance with the air concentration level determined by the dilution level determining means, a flow of the collected vapor effluents and a flow of air from the air supply means.
The invention comprises, in another form thereof, a combustion system for processing vapor emissions from a fuel receiving tank, wherein the combustion system is operatively associated with a fuel dispensing means for delivering fuel into the fuel receiving tank. The combustion system includes a vapor collection means for controllably collecting vapor emissions from the fuel receiving tank; a catalytic oxidation means for operatively catalytically oxidizing a vapor composition including a fuel component and an air component; and a temperature determining means for determining an oxidation temperature associated with the catalytic oxidizing activity of the catalytic oxidation means. A vapor mixing means is provided for controllably mixing the vapor emissions collected by the vapor collection means with a controllable amount of air, as determined by the oxidation temperature provided by the temperature determining means, to form a vapor mixture thereof having a selectable dilution level. A vapor transfer means is further provided for transferring the vapor mixture from the vapor mixing means to the catalytic oxidation means for catalytic oxidation therein.
The catalytic oxidation means includes an oxidation catalyst operative to support an oxidation reaction involving hydrocarbon. The temperature determining means includes a sensor means for sensing an operating temperature of the catalytic oxidation means. The vapor mixing means comprises, in one form thereof, a dilution level determining means for determining an air concentration level for the vapor mixture as a function of the oxidation temperature determined by the temperature determining means. The vapor mixing means further includes an air supply means for supplying a controllable flow of air. A combining means is further provided for controllably combining, in accordance with the air concentration level determined by the dilution level determining means, a flow of the collected vapor emissions and a flow of air from the air supply means.
The invention comprises, in yet another form thereof, a combustion system for processing fuel vapors contained within a fuel storage tank. The system is operatively associated with a fueling apparatus including fuel dispensing means for dispensing fuel from the storage tank to a vehicle fuel container; fuel recovery means for recovering vapor effluents from the vehicle fuel container that develop during refueling activity; and means for transferring the recovered vapor effluents, at least in part, to the storage tank.
The combustion system includes a venting means for controllably venting fuel vapors from the storage tank; an oxidation processing means for operatively oxidizing a vapor composition including hydrocarbon and oxygen; and a sensor means for sensing a temperature associated with the oxidizing activity of the oxidation processing means. A vapor dilution means, which is responsive to the temperature sensed by the sensor means, is provided for controllably diluting the vented vapor effluents as a function of the sensed temperature to form a mixture including air and vapor effluents. A vapor transfer means is further provided for transferring the air-vapor mixture from the vapor dilution means to the oxidation processing means for oxidation therein.
The oxidation processing means further includes an oxidation catalyst. The sensor means includes a means for determining the temperature of the oxidation catalyst. The combustion system includes, in another form thereof, a combustion chamber containing the oxidation catalyst. The sensor means includes, in another form thereof, a means for determining the temperature within the combustion chamber.
The invention comprises, in yet another form thereof, a method of processing vapor effluents from a fuel receiving tank. The processing method involves collecting the vapor effluents; providing an oxidation catalyst that is operative in oxidizing fuel vapors; and sensing an operating temperature of the oxidation catalyst. The collected vapor effluents are controllably diluted with an amount of air according to the sensed operating temperature of the oxidation catalyst to form a vapor mixture thereof having a selectable air concentration. The vapor mixture formed by the dilution activity is transferred to the oxidation catalyst for oxidation therein.
One advantage of the present invention is that the combustion system affords a degree of selective control over the appropriate level of dilution of the vapor effluent stream on the basis of an easily acquired measurement value (i.e., oxidation reaction temperature).
Another advantage of the present invention is that the catalytic oxidation reaction of the combustion system is capable of supporting lean mixtures of fuel vapor and air.